This invention concerns improvements in or relating to flexible joint means.
One known flexible joint means comprises an annular flexible bearing acting between confronting axially aligned ball and socket surfaces of a pair of members to accommodate relative pivotal movement between the members in any plane containing the longitudinal axis of the joint means.
A disadvantage of this type of joint means is that the flexible bearing although capable of accommodating high compression loads can only withstand relatively low tension loads before rupturing. As a result for applications where compression and tension loads of similar magnitude are to be accommodated it is necessary to provide joint means incorporating two flexible bearings arranged one to carry the compression loads and the other to carry the tension loads. This is unsatisfactory as not only is the arrangement expensive to manufacture but also an undesirable increase in the conical stiffness of the assembly arises from the use of two flexible bearings.
According to the present invention there is provided flexible joint means comprising a hollow outer member, an inner member having a body portion located within the outer member and a stem portion projecting outwards through an opening in the outer member, a flexible bearing acting between confronting surfaces on the inner and outer members and a substantially incompressible fluid contained within a fluid tight chamber within the outer member.
Joint means according to the present invention is capable of carrying both tension and compression loads, tension loads being accommodated mainly by the flexible bearing in compression and compression loads being accommodated mainly by increase in pressure of the incompressible fluid within the chamber.
Preferably the fluid within the chamber, for example gas or liquid or a combination thereof, is under pressure in the unloaded condition of the joint means, the fluid pressure serving to pre-load the flexible bearing in compression.
The degree of pre-loading of the flexible bearing is preferably chosen to lie within the operating range of the tension loads which the joint means is designed to carry. In consequence the overall working deflection of the bearing is reduced and also the occurrence of tension loads in the bearing is avoided both of which contribute to an improved fatigue life of the bearing.
Preferably the sealed chamber is defined at least in part by a control element e.g. a flexible diaphragm or slidable shuttle subjected on one side to the fluid pressure in the chamber and on the opposite side to an external fluid pressure which serves to prevent the occurrence of negative pressure in the fluid contained within the chamber. External fluid pressure may be that of a fluid surrounding the joint means e.g. atmospheric air pressure or the pressure of fluid contained within a sealed cavity acting on the opposite side of the control element to the fluid in the chamber.
Preferably the joint means is capable of accommodating relative pivotal movement between the inner and outer members. Thus the confronting axial aligned surfaces on the inner and outer members may be part-cyclindrical allowing pivotal movement in one plane containing the longitudinal axis of the joint means but more preferably the surfaces are part-spherical allowing omnidirectional pivotal movement in any plane containing the longitudinal axis of the joint means. Preferably the confronting surfaces have a common central axis (part-cylindrical) or centre of curvature (part-spherical).
The flexible bearing is preferably of laminate construction consisting of interleaving layers of elastomeric material e.g. rubber and reinforcement plates but may comprise elastomeric material alone. The bearing has end faces complementary to the profile of the confronting surfaces on the inner and outer members and where such surfaces are of curved profile and the bearing is of laminate construction the individual layers/plates of the bearing are of similar curved profile. The end faces of the bearing may be bonded to the confronting surfaces or attached to metal end rings which are secured to the surfaces by any known means. The bearing may be annular with a central opening through which the stem portion of the inner member extends and may be of unitary construction or consist of a plurality of individual segments.
For applications where the joint means is required to accommodate large conical deflection two inner members separate from one another are arranged back-to-back with the associated stem portions projecting outwards in opposite directions through respective openings in the outer member with a respective flexible bearing acting between each inner member and the outer member and a substantially incompressible fluid contained within the fluid tight chamber within the outer member and acting between the inner members.